1. Field of the Invention
The present invention relates to an antistatic resin composition, and specifically, it relates to a methyl methacrylate-styrene copolymer resin composition having antistatic properties as well as excellent appearance properties, optical properties and transparency. More specifically, it relates to a methyl methacrylate-styrene copolymer resin composition suitable for Fresnel lens sheets and light cover sheets for electronic and electric equipments which are threatened with the adhesion of dust and the like thereon.
2. Description of Related Arts
As techniques for imparting antistatic properties to a thermoplastic resin composition, various methods have heretofore been disclosed. For example, as disclosed in Japanese Patent Publication No. 37414/1989, there are known anionic surface active agents such as alkyl phosphates and polyoxyethylene alkylphosphate, and cationic surface active agents such as quaternary ammonium salts as substances capable of imparting the antistatic properties to the surface of the thermoplastic resin composition. However, these antistatic agents lave a drawback that the effect is not durable owing to their low molecular weight.
A technique of adding a substance having the antistatic properties to the thermoplastic resin composition is also disclosed in the above-mentioned publication, and as the main antistatic agents, there are known nonionic surface active agents such as polyoxyethylene alkyl ethers, polyoxyethylene alkylamino ethers and alkyl diethanoiamides. However, these nonionic surface active agents have a lower antistatic effect than the ionic surface active agents.
Furthermore, Japanese Patent Application Laid-open No. 43440/1991 discloses a method for kneading a hygroscopic compound and an antistatic agent into an acrylic resin or the like, a method for coating the resin with a surface active agent, and another method. However, the above-mentioned kneading method has a problem that appearance properties deteriorate because of poor compatibility, bad dispersion properties, the bleeding-out of the antistatic agent on the surface of the polymer material and the like.
In addition, in Japanese Patent Application Laid-open Nos. 230835/1987 and 62336/1989, it is disclosed that a phosphonium sulfonate is used as the antistatic agent in a thermoplastic resin, for example, a polyolefin such as polyethylene or polypropylene, polystyrene, polymethyl methacrylate, polycarbonate, polyethylene terephthalate, polybutylene terephthalate or polycaprolactam. In this case, the good antistatic effect can be obtained, and an inconvenience such as the bleeding-out of the antistatic agent on the high molecular material surface can be eliminated.
However, in the composition obtained by adding the phosphonium sulfonate as the antistatic agent to the thermoplastic resin which is described in Japanese Patent Application Laid-open Nos. 230835/1987 and 62336/1989, both of its total light transmittance and refractive index are not always high, and for this reason, the above-mentioned composition has not been applicable to the field of lens base materials for projection TVs in which the high total light transmittance and refractive index are required.
However, with regard to a composition obtained by adding and blending a phosphonium sulfonate as an antistatic agent to and with a thermoplastic resin such as a polycarbonate suitable for an optical use which is mentioned in the above-mentioned Japanese Patent Application Laid-open Nos. 230835/1987 and 62336/1989, an appearance failure such as whitening and the deterioration of the total light transmittance take place at the time of the manufacture of sheets.
A methyl methacrylate-styrene copolymer resin has been used in various fields because of its excellent characteristics such as high stiffness, high refractive index and low hygroscopicity, but it is devoid of the antistatic properties. On this account, restriction is put on the application of the copolymer resin to the optical field of electric appliances such as Fresnel lenses and light covers whose demand increases year by year.